As a detector for a gas chromatograph, various types of detectors have been put to practical use, such as a thermal conductivity detector (TCD), electron capture detector (ECD), flame ionization detector (FID), flame photometric detector (FPD), and flame thermionic detector (FTD). Among these detectors, the FID is most widely used, particularly for the purpose of detecting organic substances. The FID is a device that ionizes sample components in a sample gas by hydrogen flame and detects the resultant ion current. It has a wide dynamic range (the sample-concentration range within which the detection sensitivity shows a high degree of linearity) which has reached approximately six to seven orders of magnitude. However, the FID has drawbacks: firstly, its ionization efficiency is low, and therefore, its minimum detectable amount is not low enough; secondly, its ionization efficiencies for alcohols, aromatic substances, and chlorine-based substances are low; and thirdly, it requires hydrogen, which is a highly hazardous substance, and therefore, an explosion-proof apparatus or similar kind of special equipment must be provided, which makes the entire system difficult to operate.
In recent years, a dielectric barrier discharge ionization detector (which is hereinafter abbreviated as “BID”) which employs ionization by dielectric barrier discharge plasma has been put to practical use as a new type of detector for a gas chromatograph (for example, see Patent Literatures 1 and 2, as well as Non Patent Literature 1).
In the BID described in the aforementioned literatures, a low-frequency AC high voltage is applied to the discharge electrodes circumferentially provided on a dielectric quartz glass tube, whereby a predetermined gas supplied into the tube line is ionized and non-equilibrium atmospheric pressure plasma is formed. The sample components in the sample gas injected into the tube line are ionized by the effects of the light emitted from this plasma, the excited species and the like. The thereby produced ions are collected by the collector electrode, and a detection signal corresponding to the amount of ions, and hence the amount of sample components, is generated. Generally, it is said that the mechanism of the ionization of sample components in the discharge ionization detector is the photoionization by high-energy vacuum ultraviolet light radiated from the plasma and the Penning ionization by meta-stable helium atoms produced by the plasma. As for the BID, as described in Non Patent Literature 1, it has been experimentally confirmed that the photoionization by the vacuum ultraviolet light mainly contributes to the ionization of the sample components.